The present invention relates to metallocene complexes of metals of transition group IV, V or VI of the Periodic Table, in which at least one substituted or unsubstituted cyclopentadienyl radical is bound to an element of group III of the Periodic Table which is in turn a constituent of a bridge between this cyclopentadienyl radical and the metal atom and bears an organonitrogen, organophosphorus or organosulfur group as sole further substituent.
Metallocene catalysts are gaining increasing importance in the polymerization of xcex1-olefins. Metallocene catalysts are particularly advantageous for the copolymerization of ethylene with higher xcex1-olefins since they result in particularly uniform incorporation of comonomer into the copolymer. Among metallocene catalysts, bridged metallocene complexes have attracted particular interest since they generally give a higher productivity than do the unbridged complexes, result in particularly good incorporation of comonomer and are also, for example, suitable for preparing highly isotactic polypropylene.
Bridge metallocene complexes in which the cyclopentadienyl radicals are joined by SiMe2 or C2H4 bridges have been known for a long time. Such metallocene compounds are described, for example, in EP-A-336 128.
Apart from metallocene complexes in which the cyclopentadienyl radicals are bridged via silicon or carbon atoms, bridged metallocenes in which one or more boron atoms perform the bridging function are also known. Thus, for example, boron-bridged metallocene complexes in which the boron atom bears an alkyl or aryl substituent are known (J. Organomet. Chem., 1997, 536-537, 361). However, the preparation of these metallocene complexes is very complicated; nothing is known about polymerizations using these complexes.
DE-19 539 650 likewise describes bridged metallocene complexes in which boron, inter alia, may be present as bridge member. The boron atoms having a bridging function may be substituted by various radicals such as alkyl, aryl, benzyl and halogens and also by alkoxy or hydroxy groups. Once again, nothing is known about the polymerization behavior of such metallocene complexes.
Organometallics, 1997, 16, 4546, describes boron-bridged metallocenes in which the bridging boron atom is substituted by a vinyl group and is additionally coordinated by a Lewis base. However, the yields in the synthesis of these complexes are very poor and the polymerization of ethylene proceeds unsatisfactorily and leads only to low molecular weight polymer.
EP-A-0 628 566 describes bridged metallocene complexes whose generic formula nominates carbon, silicon, tin, germanium, aluminum, nitrogen, phosphorus and also boron as bridging atoms and in which the bridging atoms may be substituted by many substituents among which the dialkylamino group is mentioned. However, metallocene complexes having an amino-substituted boron bridge are not explicitly mentioned at any point, nor are properties of such complexes described.
The boron-bridged metallocene complexes known from the prior art are mostly difficult to prepare and do not offer, of offer only to a very restricted extent, the opportunity of influencing the electronic conditions in the cyclopentadienyl groups by means of electron-donating substituents on the boron atom and thus making it possible to influence the catalytic activity of the complexes.
It is an object of the present invention to provide metallocene complexes which no longer have the disadvantages described, are simple to prepare and, in particular, offer the opportunity of influencing the electronic conditions on the cyclopentadienyl radicals.
We have found that this object is achieved by the metallocene complexes mentioned at the outset. Furthermore, we have found a process for preparing such metallocene complexes and the use of the metallocene complexes as catalyst components for the homopolymerization and copolymerization of C2-C10-xcex1-olefins.
As element of group III of the Periodic Table, particular mentioned may be made of boron and aluminum, with boron being particularly preferred.
Among the substituents which can act as the sole further substituent which occupies the third valence of the element of group III of the Periodic Table in addition to the bonds to a cyclopentadienyl radical and the other constituents of the bridge, particular mention may be made of organonitrogen, organophosphorus or organosulfur groups which, in addition to these heteroatoms, comprise up to 20 carbon atoms and up to 4 silicon atoms.
The metallocene complexes of the present invention may contain 1 or 2 cyclopentadienyl radicals. Preference is given to metallocene complexes of the formula I 
where the variables have the following meanings:
M is a metal atom of transition group IV, V or VI of the Periodic Table,
D is an element of group III of the Periodic Table,
R1,R2,R3,R4 are each hydrogen, C1- to C10-alkyl, 5-7-membered cycloalkyl which may in turn bear a C1-C10-alkyl group as substituent, C6- to C15-aryl or arylalkyl, where two adjacent radicals R1 to R4 may also form 5-7-membered cyclic groups which may in turn bear C1-C10-alkyl groups or SiR63 groups as substituents or include further fused-on ring systems,
R5 is hydrogen, C1-C10-alkyl, C6-C15-aryl or -arylalkyl or C1-C10-trialkylsilyl,
R6 is C1-C4-alkyl,
m is the number of the transition group of the metal atom M minus 2,
n is 2 when X1 is nitrogen or phosphorus and is 1 when X1 is sulfur,
X1 is nitrogen, phosphorus or sulfur,
X2 is hydrogen, C1-C10-hydrocarbyl, N(C1-C15-hydrocarbyl)2 or halogen,
A is a radical 
xe2x80x83or a radical which is coordinated to M via an oxygen, sulfur, nitrogen or phosphorus atom.
Suitable metal atoms M are, in particular, the elements of transition group IV of the Periodic Table, i.e. titanium, zirconium and hafnium, with titanium and zirconium being preferred and zirconium being particularly preferred.
The cyclopentadienyl groups in formula I may be substituted or unsubstituted. Among the substituted metallocene complexes, those which are substituted by C1-C4-alkyl groups display particularly advantageous properties. Possible alkyl substituents are, for example, methyl, ethyl, n-propyl and n-butyl. The cyclopentadienyl radicals can be monosubstituted or polysubstituted, with monosubstituted and disubstituted cyclopentadienyl radicals having been found to be particularly advantageous. Preference is also given to cyclopentadienyl radicals in which 2 adjacent radicals R1 to R4 are joined to form 5- to 7-membered cyclic groups. Examples which may be mentioned are cyclopentadienyl groups derived from indenyl, tetrahydroindenyl, benzindenyl or fluorenyl, with these ring systems in turn being able to be substituted by C1-C10-alkyl groups or by trialkylsilyl groups.
In the metallocene complexes of the present invention having 2 cyclopentadienyl units, the bridging atom of the element of group III of the Periodic Table is directly bound to these two cyclopentadienyl units.
Among these dicyclopentadienyl complexes, particular preference is given to metallocene complexes in which
A is a radical 
In the case of monocyclopentadienyl complexes, on the other hand, the radical A is not a cyclopentadienyl radical but rather a radical which is coordinated to M via an oxygen, sulfur, nitrogen or phosphorus atom. Possible groups A are, in particular, the following atoms or groups: xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NR9xe2x80x94, xe2x80x94PR9xe2x80x94 and uncharged 2-electron donor ligands such as xe2x80x94OR9, xe2x80x94SR9, xe2x80x94NR92 or xe2x80x94PR92. In these formulae, R9 is hydrogen or an alkyl, aryl, silyl, halogenated alkyl or halogenated aryl group having up to 10 carbon atoms. Particular preference is given to metallocene complexes in which A is a group
xe2x80x94ZR72xe2x80x94NR8xe2x80x94
in which
Z is silicon or carbon and
R7,R8 are hydrogen, silyl, alkyl, aryl or combinations of these radicals having up to 10 carbon or silicon atoms.
Examples of radicals R7 and R8 are, in particular, hydrogen, trimethylsilyl, methyl, tert-butyl and ethyl. Z is preferably a carbon atom.
In the metallocene complexes of the present invention, the bridging atom of the element of group III of the Periodic Table, which in itself has Lewis acid character, is substituted by a compound having Lewis base character. Due to its electron donor function, the Lewis base substituent influences the electronic conditions on the cyclopentadienyl radical and thus also the electronic environment of the metal atom. The Lewis base substituent can be bound to the bridging atom of the element of group III of the Periodic Table via a nitrogen, phosphorus or sulfur atom, with substituents having a nitrogen atom being particularly preferred. The atom X1 can bear either hydrogen, C1-C10-alkyl groups or C1-C10-trialkylsilyl groups. Suitable alkyl groups are, in particular, C1-C4-alkyl groups and very particularly methyl or ethyl groups.
The central atom M is substituted not only by the ligands mentioned but also by ligands X2. Suitable ligands X2 are, in particular, lower alkyl groups such as methyl and ethyl, but X2 is preferably halogen, particularly preferably chlorine.
The metallocene complexes of the present invention can be prepared in various ways. In the case of compounds having a bridging boron atom, for example, a method which has been found to be advantageous for preparing such metallocene complexes is to react a compound R5nX1xe2x80x94BY2 (II), where Y is halogen, with a compound 
where Mxe2x80x2 is an alkali metal or alkaline earth metal, in the presence of a metal alkyl and then to allow the reaction product to react with an M halide compound and finally with an oxidant.
In formula (II), Y is preferably chlorine. The preparation of compounds of the formula (II) is described, for example, in Angew. Chem. 1964, 76, 499. The synthesis of the metallocene complexes of the present invention according to the above-described process is particularly simple and can be carried out in only one reaction vessel. The metal alkyl serves as deprotonating reagent; preference is given to using alkali metal alkyls or alkaline earth metal alkyls, in particular butyllithium. Suitable M halide compounds are, for example, titanium trichloride derivatives, particularly preferably titanium trichloride tris(THF) adduct. As oxidant in the final oxidation reaction, it is possible to use, for example, lead dichloride. After filtration of the reaction mixture, the metallocene complex can be isolated from the solution.
The metallocene complexes of the present invention can be used as catalyst components for the homopolymerization and copolymerization of C2-C10-xcex1-olefins. To carry out the polymerization, it is generally necessary to convert the metallocene complexes into a cationic complex by means of suitable compounds capable of forming metalloceniuim ions. Possible compounds capable of forming metallocenium ions are, for example, aluminoxanes, preferably ones having a degree of oligomerization of from 3 to 40, particularly preferably from 5 to 30.
Apart from aluminoxanes, further cation-forming compounds are, in particular, borane and borate compounds which are a noncoordinating anion or can be converted into such an anion and form an ion pair with the metallocenium complex. Suitable reagents of this type for activating the metallocene complexes are well known to those skilled in the art and are described, for example, in EP-B1-0468537.
Particularly for polymerizations in the gas phase and in suspension, it may be necessary to apply the metallocene complexes and possibly the activating reagents to support materials. Such support materials and methods of applying catalyst complexes to supports are well known to those skilled in the art. Suitable support materials are, in particular, inorganic oxides such as silica gel, aluminum oxide or magnesium salts.
The above-described catalyst systems make it possible to prepare polyolefins, in particular polymers of 1-alkenes. For the purposes of the present invention, these are homopolymers and copolymers of C2-C10-alk-1-enes, with preferred monomers being ethylene, propylene, 1-butene, 1-pentene and 1-hexene. These catalyst systems are particularly useful for polymerizing ethylene with 1-butene or 1-hexene.
As polymerization processes, it is possible to employ all known processes, i.e., for example, gas-phase processes, suspension processes or polymerization processes in solution.
When used for the polymerization of ethylene and the copolymerization of ethylene with other xcex1-olefins, the metallocene complexes of the present invention display good polymerization activity and lead to polymers having a relatively high molecular weight. The following examples illustrate the invention.